EAGER: Scanning Ultrasound Probe for Semiconductor Sub-Surface Metrology

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Non-technical:There is an acute need to image semiconductor devices at nanometer scales below the surface. This will make it possible to identify buried defects and perform failure analysis in two- and three-dimensional structures such as micro-electromechanical systems (MEMS). Current nanoscale subsurface imaging techniques require extensive sample preparation, are exceptionally slow, and require expensive equipment. Or they are simply unable to image opaque samples. The solution is a tool which provides non-destructive, high throughput nanoscale imaging of buried defects at a reasonable cost. This project will combine scanning probe microscopy with ultrasound holography to reveal and characterize subsurface features with nanoscale resolution in three dimensions. In this technology, a cantilever monitors acoustic waves that travel along the surface. Perturbations to the amplitude and phase of these waves carry information about structures beneath and near the surface. These variations are detected as small differences in frequency and phase, resulting in beats that are detected by the cantilever. These variations are then used to create spatial mappings generated by subsurface and near-surface features and defects as the cantilever scans across the surface. The ultimate aim is to integrate scanning probe microscopy hardware with functional electronics into field-programmable gate arrays, configurable integrated circuits. The project promises to open new vistas in non-destructive imaging of semiconductor devices and structures. Once developed, the technology will be made available to other institutions, broadening the user base to include physical sciences, engineering and related fields. The PI will integrate results from this project into undergraduate courses and highlight how the principles of engineering and physical science impact materials and device research. Active participation of underrepresented groups will be promoted through classroom visits to elementary schools through the Science Chicago program.Technical:There is an acute and timely need for innovative imaging modalities in semiconductor industries. These are especially needed to identify the buried defects and delamination and provide failure analysis in both two- and three-dimensional structures. These include devices based on micro-electromechanical systems (MEMS) and interconnects. This project will develop "Scanning Thickness Resonance Acoustic Microscopy" for sub-surface inspection and failure analysis. Current nanoscale subsurface imaging techniques are unable to probe optically opaque samples or require extensive and time consuming sample preparation, are exceptionally slow, and require expensive metrology equipment. The solution is a tool which provides non-destructive, high throughput nanoscale imaging of buried defects, and that can be widely deployed at multiple points in the research and development cycle, at a reasonable cost. Anticipated applications will identify buried nanostructures in semiconductor, MEMS, and low-K dielectric materials both in 2D and 3D geometries. This innovative technology will bring transformative research in identifying the failure analysis and buried defects both in 2D and 3D materials stacks in complex three-dimensional devices and structural geometries with nanometer scale resolution. In this technology, the cantilever monitors the perturbation to the surface acoustic waves, especially their phase, which carry information about embedded or buried sub-structures reflected in the scattering of specimen acoustic waves due to the difference in their respective viscoelastic properties. Variations in the amplitude and phase of the bulk wave due to the presence of the sub-surface nanostructures/defects as well as the variations in near surface affect the amplitude and the phase of the difference frequency signal (beats) which is detected by cantilever. These variations are used to create spatial mappings generated by subsurface and near-surface features/defects. To realize these efforts requires a way to combine scanning probe microscopy hardware, functional electronics and its integration into field programmable gate arrays for simultaneous generation and detection of multiple harmonics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.